The present invention is directed to an energy absorbing device comprising slow recovery viscoelastic polyurethane foam with a surface impregnation of material for preventing the absorption of moisture.
Head injuries are a leading cause of death and disability in the United States. Data collected by the Centers for Disease Control demonstrate that, on average, three hundred thousand sports-related brain concussions occur in the United States each year. Children under the age of fourteen have a greater risk for concussions than do adults. Teenagers that suffered two or more “big hits” to the head can suffer long-term damage to their thinking abilities. Twenty percent of teenagers that have suffered multiple concussions have continuous headaches and suffer sleep and concentration disorders. The damage from concussions can vary from mild, which is completely reversible, to severe which can lead to coma or death.
A concussion is an injury to the brain cells resulting from trauma to the head. Loss of consciousness is not necessary for a head injury to be considered a concussion. Concussions are graded in severity on a scale of Grade One (mild) to Grade Three (severe). Concussions are considered to be Grade One when there is no loss of consciousness and symptoms last less than fifteen minutes. A Grade Two concussion is when there is no loss of consciousness, with symptoms lasting longer than fifteen minutes. A Grade Three concussion is when there is any loss of consciousness.
Though the incidence of concussions at the amateur levels of ice hockey are not known, it is thought to be a fairly common occurrence. A hockey study from Canada surveying players throughout all professional levels in the sport demonstrated that at least sixty percent of the players suffered at least one concussion in their career. From Oct. 1, 2001 through Dec. 31, 2001, there were sixty-seven concussions in the National Hockey League. The total number of concussions in the National Hockey League exceeds one hundred per year for a league that has six hundred players.
The governing bodies at every level of amateur and profession ice hockey mandate the use of helmets. Typically, helmets comprise a rigid outer shell and an energy absorbing liner. The helmet shell functions to: (i) maintain the energy absorbing liner in position upon impact, (ii) prevent penetration of sharp objects, and (iii) dissipate the impact's energy prior to it reaching the energy absorbing liner.
Energy absorbing liners and padding are made from either open-cell foam or closed-cell foam. Energy absorbing liners and padding compress as they absorb energy. The purpose of the energy absorbing liner is to decrease the energy of the impact force. This is called impact attenuation. If an egg were dropped onto an energy absorbing pad, it would either crack or stay whole, based on the amount of energy absorbed by the energy absorbing padding. Open-celled foam will rebound after it is compressed from an impact. Polyvinyl chloride padding or vinyl nitrile padding are types of celled foam commonly used in helmets as an energy absorbing liner. Expanded polystyrene (EPS) is a type of closed-cell foam that is the most commonly energy absorbing liner used today in sporting helmets. EPS is a type of STYROFOAM used for packaging protection. EPS is compressed and crushed as it absorbs energy. While EPS attenuates impact force well and is considered the “gold standard” in the helmet market, impacts produce permanent damage to the EPS material. Minor impacts to the helmet shell cause microscopic cracks in the EPS, which can seriously destroy its impact attenuation performance.
Most urethane foams are elastic in that the foam deflects under a load, and return a force to the load that is equal to the deflection of the elastic material multiplied by its stiffness. When pressure is applied to common urethane foam, like a spring, the foam deflects and returns a force that is proportional to the amount of deflection. Areas of greatest deflection (i.e., greatest pressure) receive the greatest return force. These pressure hot spots can restrict blood circulation to portions of the body.
Viscoelastic foams have both viscous and elastic response properties. The viscous response property evenly distributes a load, and the elastic response property allows the foam to support a static load. “Viscous” refers to a fluid response that flows away from the applied load or applied force, in that the fluid redistributes the applied load or applied force. Viscoelastic materials redistribute the applied load or applied force away from the point of contact.
Slow recovery viscoelastic polyurethane foam molds, shapes, and adjusts to the surface it is in contact with the application of heat. In athletic headgear, for example, the athlete's head causes the application of heat to the slow recovery viscoelastic polyurethane foam. CONFOR foam displays this characteristic greater than other viscoelastic polyurethane foams. Typically, athletic headgear comprises an outer shell and an inner energy absorbing liner for absorbing impacts suffered during the course of an athletic contest. An energy absorbing liner comprising viscoelastic polyurethane foam absorbs energy transferred from the outer shell, if the head represents the final transfer point of the impact energy. Naturally, the viscoelastic polyurethane foam should absorb as much impact energy as possible prior to being completely compressed. Of course, the greater the surface area of the viscoelastic polyurethane foam contacting the skull, the greater the energy dissipation and absorption there will be prior to the viscoelastic polyurethane foam reaching maximum compression (bottoming out). The viscoelastic polyurethane foam should return to its pre-impact shape after the impact.
Preferred foams would be CONFOR foam by E-A-R Specialty Composites, a division of Cabot Safety Corporation, preferably the stiffer grades such as green or blue would be used for protection of high impact regions but lower densities such as yellow and pink could be used for appropriate uses. Other preferred foams are the Sunmate brand foam from Dynamic Systems, Inc. and Tempur brand foams from Fagerdala World Foams of Sweden.